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The Physics of Breathing Underwater

On a daily basis, most of us don't really pay attention to our breathing as we go about a number of routine tasks. However, it is a very different story when we are submerged in water. Suddenly we are all too aware of how difficult it is to breathe. Like other land mammals, humans cannot breathe underwater. When we swim, we need to hold our breath. On the other hand, fish and sea mammals have specially adapted systems that do allow them to breathe underwater or stay submerged for a long time without breathing. In the case of fish, they do need oxygen to survive, but cannot inhale the way we do. Instead, they rely on dissolved oxygen that exists in the water. Water flows in through the mouth and over the gills. The gills absorb any available oxygen from the water and filter the rest out. Those who keep pet fish may observe that they often tend to open and close their mouths as they swim to aid in the respiratory process. Larger fish that require higher oxygen levels may leave their mouths open for a longer time to allow more water to enter. Many marine mammals, like whales, seals, and dolphins need to surface for air. Even so, they respiratory systems are adapted in a way that allows them to retain oxygen for a long time, enabling them to dive deep without ill effects.

In the earliest days of undersea exploration for humans, they had to simply hold their breath and resist from diving too deep. Prototypes of the modern day snorkel allowed divers to keep their faces submerged near the surface, while observing underwater. The next significant advance was diving bells. It was a bell-shaped chamber that was lowered into the water with the open side facing down. The diver could then go in and out of the chamber for a breath of air as they required. While this system was certainly an improvement over any existing methods, the real mark of progress was the invention of the scuba system. Scuba divers are equipped with a large metal tank that typically contains a diluted mixture of helium and oxygen. A hose running from the tank to the breathing apparatus, known as the regulator, allows oxygen to pass into the diver's mouth. This system is now in common use among professional and leisure divers, since it allows them a high degree of flexibility. Of course, there are still risks associated with humans breathing underwater. As we move deeper below, water pressure increases and compresses the lungs. This means that the air inside the lungs is also compressed. When the diver beings to ascend, they must do so very slowly to give their lungs time to expand gradually and naturally. Ascending too fast would cause the air inside the body to expand faster than the lungs can. This could lead to traumatic internal injury or even death. While the ability to breathe underwater is exciting and convenient, we must also take necessary precautions to stay safe.

How Sea Creatures Breathe Underwater

Elephant Seals - Elephant seals are unique because they can survive on extremely low levels of oxygen for a much longer time than other mammals.

Marine Mammals - Marine mammals have developed in special ways that allow them to dive very deep without succumbing to brain or lung damage.

How Fish Breathe - Fish use their gills to filter dissolved oxygen molecules from the water as they breathe.

Whale Breathing - Whales are only able to breathe along the water's surface, so they have to use oxygen much more efficiently than land creatures.

Sea Turtles - Sea turtles have lungs that are quite similar to those of humans. They surface to breathe, but can also absorb oxygen through the cloaca (located at the end of their digestive tracts) in low-oxygen situations.

How Humans Breathe Underwater

Scuba Regulators (PDF) - This presentation demonstrates how regulators (the mouth piece) of a scuba system delivers air to the diver.

Diving Bells - In the earliest days of underwater exploration, people used diving bells that enabled them to work in a safe air space.

What is Scuba Tanks? - Scuba tanks do not contain completely pure oxygen, since that would actually be dangerous for humans. Instead, they contain a safe dilution of oxygen and helium.

Open and Closed Scuba - Learn about the differences in open and closed scuba rigs, and how air is used different in each case.

The Aqua Lung - Two French men named Jacques Cousteau and Emile Gagnan were responsible for revolutionizing technological advances that allow humans to breathe underwater for extended periods of time.